Global climate change is expected to have impacts on the physiological, phenological, and morphological traits of plants. However, the vulnerability of tropical plant reproductive processes in response to climate change events has been poorly studied. Here, we assess if warming and elevated CO₂ compromise the pollen characteristics of Stylosanthes capitata Vogel, a tropical legume forage species. This work was conducted in a Trop-T-FACE (combined Free-Air Temperature Controlled Enhancement and Free-Air Carbon Dioxide Enrichment) facility, where we exposed the plants to four treatments: C (Control-ambient atmospheric carbon dioxide concentration [CO₂] and ambient temperature); eCO₂ (increase in [CO₂] to 600 ppm and ambient temperature); eT (canopy temperature increase by 2°C and ambient [CO₂]); and eCO₂+eT, a combination of both treatments. We analyzed pollen morphology of samples taken from the different treatments through light microscopy (LM) and scanning electron microscopy (SEM). In addition, pollen viability was analyzed through colorimetry. Based on the histological LM analysis, the tapetum cells of pollen sacs showed early degeneration under eT (72%) added to hypertrophy under eCO₂ (67%) and eCO₂+eT (90%) treatments. SEM images showed compaction of pollen exine and less distinguishable pollen apertures in the treated plots (eCO₂, eT, and eCO₂+eT), possibly, by the early death of the tapetum cells. These morphological abnormalities may hinder the viability of pollen grains, as observed especially in the eCO₂+eT treatment (%V=64%) that was the lowest in comparison with the Control (71%) and the other treatments (eCO₂ = 69%, eT = 67%). These results indicate that during the reproductive cycle of S. capitata pollen sacs and pollen grains are vulnerable to warming, elevated CO₂, and their combined effects.

预计全球气候变化将对植物的生理、物候和形态特征产生影响。然而，热带植物繁殖过程对气候变化事件的脆弱性研究很少。在这里，我们评估了气候变暖和 CO ₂升高是否会影响柱花草（一种热带豆科植物草料）的花粉特征。这项工作是在 Trop-T-FACE（组合自由空气温度控制增强和自由空气二氧化碳富集）设施中进行的，在那里我们将植物暴露于四种处理：C（控制环境大气二氧化碳浓度 [CO ₂ ] 和环境温度）；生态环保₂（增加 [CO ₂ ] 至 600 ppm 和环境温度）；eT（冠层温度升高 2°C 和环境温度 [CO ₂ ]）；和eCO ₂ + eT，这两种治疗方法的结合。我们通过光学显微镜 (LM) 和扫描电子显微镜 (SEM) 分析了从不同处理中采集的样品的花粉形态。此外，通过比色法分析花粉活力。基于组织学 LM 分析，花粉囊绒毡层细胞在eT (72%)下显示早期变性，在eCO ₂ (67%) 和eCO ₂ + eT 下肥大(90%) 治疗。SEM 图像显示，处理过的地块（eCO ₂、eT和eCO ₂ + eT）中的花粉外壁被压实，花粉孔不太明显，这可能是由于绒毡层细胞过早死亡所致。这些形态异常可能会阻碍花粉粒的活力，特别是在eCO ₂ + eT处理 (%V=64%) 中观察到的，与对照(71%) 和其他处理 ( eCO ₂  = 69 )相比最低%，eT  = 67%）。这些结果表明，在S. capitalata的生殖周期中花粉囊和花粉粒易受变暖、CO ₂升高及其综合影响的影响。